The destruction and transformation of almost all toxic and non-toxic organic compounds in the environment is highly dependent on microbial activity. Anaerobic habitats are widely distributed in soils, sediments, subsurface environments and groundwater and receive significant levels of contaminants. Transformations under anaerobic conditions, particularly of the refractory aromatic hydrocarbons such as the benzenes is a poorly understood process. It is proposed the anaerobic microbial degradation of benzene, toluene and xylenes may be an important process of detoxification or transformation of these toxic organic contaminants. Because microbial degradation is so widespread, the projects and metabolites of degradation, and not the parent compound, may in fact be major components by which human health is affected. Using protocols previously developed in our laboratory, three different anaerobic conditions, denitrifying, sulfate reducing and methanogenic, will be studied, which nitrate, sulfate and carbonate serve as electron acceptors and are reduced to nitrogen, sulfide and methane, respectively. The rate, extent and metabolites produced from benzene, toluene and xylenes under each reducing condition will be examined. Furthermore, the effect of additional inorganic toxicants such as chromate, mercury and methylmercury on the degradation process will be examined. The pathway for catabolism will be delineated for on or more of the compounds with regard to metabolites formed and the relationship between stoichiometry of substrate oxidation and reduction of inorganic electron acceptor. Pure cultures of anaerobic species mediating this transformation will be isolated for separate physiological genetic and biochemical studies. Enhancement of the degradative capabilities of selected anaerobic strains will be carried out by the transfer of catabolic genes whose gene products do not require oxygen. Strains will be further improve by transferring metal resistant genes into the degradative species. Results anticipated will contribute important new knowledge concerning the anaerobic metabolism and detoxification processes of hazardous chemicals which occur in the environment and will generate bacterial strains which may be useful for decontamination purposes.